The present invention relates generally to the field of ortho-mode transducers, and, more particularly, but not by way of limitation, to an ortho-mode transducer that includes a hybrid tee waveguide junction connected to a single-polarized port of the transducer.
Ortho-mode transducers (OMTs) are commonly used in communications systems because of their ability to provide for a concurrent transmission of signals of differing frequencies and differing polarizations. As such, an OMT is an important waveguide device in dual polarized reflector and horn antenna systems.
An OMT is a three-port waveguide device that supports signals having two orthogonal modes; for example, a vertically polarized mode (V-mode) and a horizontally polarized mode (H-mode). The OMT includes a common port that supports both H-polarized and V-polarized signals, a through or back port that is axially aligned with the common port and supports only V-polarized signals, and a side port that supports only H-polarized signals.
An OMT is frequently used to separate H-polarized and V-polarized signals from a combined signal. For example, a combined signal can be received from a parabolic reflector or the like, and applied to the common port through a feed horn. The combined received signal is separated by the OMT into separate V-polarized and H-polarized signals that are output via the back and side ports, respectively. An OMT is also used in applications in which the back and side ports function as input ports and the common port functions as an output port. For example, the input ports can be coupled to sources of electromagnetic radiation and the common output port can be coupled to a receiver. Yet further, an OMT can be used in applications in which both transmitted and received signals are simultaneously guided through the OMT. For example, V-polarized signals can be transmitted and H-polarized signals can be received.
A survey of OMT technology is provided in the publication: Uher, et al, xe2x80x9cWaveguide Components for Antenna Feed Systems: Theory and CADxe2x80x9d, Artech House, Norwood, Mass., Section 3.8, 1993. In this survey, various narrowband OMTs are categorized into four basic design types including taper/branching, septum/branching, acute angle or longitudinal ortho-mode branching, and short-circuited common waveguide design types. Various broadband OMT designs are also discussed and are categorized into two main types including distinct dual junction and equal dual junction types.
Exemplary OMT transducers are set forth and described in U.S. Pat. Nos. 4,176,330; 5,392,008; 6,031,434 and 6,225,875. A further example of an OMT transducer is described in U.S. Pat. No. 6,087,908 wherein a planar OMT is constructed with the H and V ports both lying in a plane. The plane is substantially orthogonal to the common port. The common waveguide is terminated in an appropriately placed short which forces the energy into the H and V ports.
Also known in the art are OMTs that are often referred to as xe2x80x9csplitxe2x80x9d OMTs. A split OMT is an OMT that is assembled from two, separately manufactured parts or halves. In particular, the manufacture of an OMT involves the precise assembly of a variety of elements; and, as a result, the manufacture of an OMT as a single component is often quite difficult and costly. In a split OMT, on the other hand, the OMT is constructed from two halves that are separately manufactured and that are designed to be symmetrical with respect to their longitudinal plane of assembly so that the halves may be easily assembled into a finished OMT. The separate halves are capable of being manufactured using common industrial processes such as machining, casting or molding; and, thus, are usually easier and less costly to manufacture. Also, because the halves can be manufactured using common processes, split OMTs are usually capable of being produced on a considerably larger scale than one-piece OMTs.
A discussion of split OMTs is provided in the publication: M. Ludovico, et al, xe2x80x9cCAD and Optimization of Compact Ortho-mode Transducersxe2x80x9d, IEEE Trans. Microwave Theory and Techniques, December 1999, pp 2479-2485. In addition, various split OMTs and other waveguide components are described in U.S. Pat. Nos. 4,516,089; 5,243,306 and 5,576,670. In U.S. Pat. No. 4,516,089, for example, a waveguide device is described that is constructed from two half shells which are symmetrical with respect to a longitudinal plane of the device and that are assembled together using attachment screws. U.S. Pat. No. 5,243,306 describes a branching filter which comprises a transmit filter, a waveguide branching filter and a receive filter. Each of the filters are divided into first and second parts, and various ones of the parts are formed integral with other parts so as to facilitate manufacture of the branching filter. U.S. Pat. No. 5,576,670 describes a known branching filter for a transmitter-receiver that is constructed in three parts that are detachably connected together to provide the device.
Various other waveguide devices and components are described in U.S. Pat. Nos. 2,730,677; 2,766,430; 3,670,268; 4,047,128; 4,074,265; 4,302,733; 4,413,242; 4,420,756; 4,849,761; 5,066,959 and 5,075,647. Several of these patents, for example, U.S. Pat. Nos. 2,766,430; 3,670,268 and 4,413,242, describe a waveguide device that is sometimes referred to as a hybrid tee waveguide junction or a xe2x80x9cmagic tee waveguidexe2x80x9d, while others of the patents, for example, U.S. Pat. Nos. 4,420,756; 4,489,761 and 5,066,959, describe various systems that incorporate such a device. Hybrid tee waveguide junctions are frequently used as power dividers or power combiners and will be described in greater detail hereinafter.
Known OMTs are not fully satisfactory for a number of reasons. For example, some OMT designs are not fully effective in preventing the generation of undesirable higher order modes. Other OMT designs do not provide a sufficiently high isolation between the side and back ports, particularly those OMT designs that endeavor to provide a compact construction. Yet other designs, as indicated above, are difficult to manufacture and are thus relatively expensive.
It would be a distinct advantage, therefore, to provide an OMT that is compact and low in cost and that also provides a high degree of isolation, excellent mode purity and acceptable return loss levels.